Organofluorine chemistry plays an importance role in medicinal, agricultural, and material sciences and fields. Fluoroalkyl groups have strong effects such as high stability and lipophilicity, in addition, longer fluoroalkyl groups have high water-, oil-resistance and low fricition.
Homogeneous catalysis still suffers from the inherent problems associated with homogeneous catalyzed reactions due to the use of unrecoverable metals and ligands, as well as inconveniences with regard to catalyst handling, recyclability, and separation of the catalyst from products, impede the transfer of these advances to large-scale industrial processes. Furthermore expensive and structurally complicated ligands are required in homogeneous catalysis, which are often not even comnmercially available for use on industrial scale.
EP 0 114 359 A1 discloses a process for the manufacture of perfluoralkyl substituted carbocyclic or heterocyclic compounds by reaction of perfluoroalkyl iodides with unsubstituted or substituted carbocyclic or heterocyclic compounds at elevated temperatures and in presence of at least one alkaline salt, characterized by carrying out the reaction in the presence of at least one metal of the first or eight auxiliary group of the periodic table or in the presence of a complex compound containing said metal as the central atom.
The examples show the use of K2CO3 as base and reaction temperatures of 150° C., 160° C. and 170° C. for the heterogeneously catalyzed reactions. For the preparation of C8F17—C6H5 in Example 1 using a Ru/C catalyst a yield of 89.2% is disclosed.
In case of Pt/C in examples 5 to 7 a yield of 55 to 76 mol % is disclosed for the conversion of benzene with three different perfluoroalkyl iodides.
WO 93/16969 A discloses a process for the catalytic perfluoroalkylation of aromatic compounds, wherein a perfluoroalkyl iodide or mixture of iodides is reacted with an aromatic compound in the presence of an aqueous base, such as an alkali metal hydroxide or carbonate, and discloses that further improvements in rate and yield are secured by employing, as the catalyst, a noble metal supported on porous silica microspheres.
The examples show the use of K2CO3 and KOH as bases and reaction temperature of 170° C., 180° C. and 200° C.
Example 1 reports a yield of 93% using a catalyst consisting of 2% Pd and 0.1% Pt on a silica support.
The use of a support different from silica is reported in example 2, 17 and 18, example 2 discloses a yield of only 55% using 5% Ru/C as catalyst, example 17 and 18 disclose a yield of only 4.5% and 2.5% respectively using 2% Pd/C as catalyst.
Example 19 and 20 disclose the use of 5% Pd and 1% cobalt respectively on high surface area carbon (surface area 2000 m2/gram) and a yield of 87% and 88% respectively.
A special procedure for the preparation of the silica supported catalyst is disclosed.
EP 1 947 092 A1 discloses perfluoroalkylation of nucleobases with a perfluoroalkyl halide in the presence of a sulfoxide, a peroxide and an iron compound. A specifically mentioned catalytic system is a Fe2(SO4)3/H2SO4/H2O2 system.
There was a need for a heterogeneously catalyzed process for the preparation of perfluoroalkylated compounds, which provides high yields, which does not require high temperatures and does not require the use of catalysts prepared according to special procedures. The method should be applicable to a wide variety of substrates and should be compatible with a wide variety of functional groups. Furthermore the method should not be restricted to iodides as alkylating agent only, but should also work with other halides. And the method should work not only with perfluorinated alkyl iodides, but also with fluorinated and chlorinated alkyl halides.
Unexpectedly the use of Cs2CO3 or CsHCO3 as base together with Pt/C as catalyst meets these requirements. No dialkylated products are observed. The reaction does not mandatorily require inert atmosphere but can even be done under air atmosphere. The catalyst can be reused and is not deactivated by the reaction.
Compared to prior art, various advantages are observed as outlined in the examples below, e.g. in case of naphtalene not only the yield is higher but also the selectivity is better, only the alpha position is substituted. The method is applicable both to aromatic and non-aromatic compounds. Also heteroaromatic compounds can be converted, even nonactivated thiophenes react smoothly at comparably low temperatures, n-methyl pyrrole reacts under mild conditions at 50° C. Also the notoriously difficult pyridines, which are very stable to many alkylating reagents and even can be used as a solvent in some perfluoroalkylation reactions, were converted with high yields. Also with caffeine high yields are obtained.
In this text, the following meanings are used, if not otherwise stated:    alkyl linear or branched alkyl;    DBU 1,8-diazabicyclo[5.4.0]undec-7-en    halide F−, Cl−, Br− or I−, preferably Cl−, Br−, and I−, more preferably Br− and I−;    halogen F, Cl, Br or I; preferably F, Cl or Br; more preferably F or Cl;    HRMS EI: High Resolution Mass Spectrometry Electron Impact    “linear” and “n-” are used synonymously with respect to the respective isomers of alkanes;    MTBE methyl tert-butyl ether;    Pt/C platinum on charcoal    RT room temperature, it is used synonymously with the expression ambient temperature;    THF tetrahydrofurane    “wt %”, “% by weight” and “weight-%” are used synonymously and mean percent by weight.